Equalizing the electric field intensity within chick brain immersed in buffer solution at different carrier frequencies

Presented here are the numerical relationships between incident power densities that produce the same average electric field intensity within a chick brain half immersed in buffered saline solution and exposed to a uniform electromagnetic field at carrier frequencies of 50, 147, and 450 MHz. Calculations are based on modeling the buffer solution as a spherical shell in air with an inner concentric sphere of brain tissue. The results support our earlier conclusion that calcium efflux results obtained at different carrier frequencies are in agreement when related by the electric field within the brain.     

A scheme for incorporating DC magnetic fields into epidemiological studies of EMF exposure

Experimental data on calcium-ion release in chicken brain tissue suggest that biological effects of electric and magnetic fields (EMFs) are concentrated near certain “active combinations” of DC magnetic field strength and “effective” AC magnetic field frequencies. We hypothesize that active AC/DC combinations may exist and suggest that epidemiologic data, coupled with DC magnetic field measurements, may be used to identify critical exposure conditions. An empirical model is used to calculate these multiple active combinations at any given DC magnetic field strength and to define a rating system that incorporates the proximity of AC magnetic field frequencies generated by electric power lines to the new, computed effective frequencies. Such an exposure score may be useful in investigating correlations of EMF exposure with disease incidence. For 60 Hz and 50 Hz, the highest EMF exposure scores occurred at DC field strengths of 506 mG and 422 mG, respectively. The exposure score contains a factor which may be adjusted to reflect the importance of harmonics of the AC magnetic field as well as of the fundamental frequency. Using this factor, we consider two important special cases consistent with chick brain data: 1) we consider active pairs associated with all detectable harmonics (up to 660 Hz) without regard to relative intensity of the harmonics, and 2) we use the relative intensities of the AC field frequencies to adjust their contribution to the exposure score. © 1993 Wiley-Liss. Inc.     

Current density in a model of a human body with a conductive implant exposed to ELF electric and magnetic fields

A numerical model of a human body with an intramedullary nail in the femur was built to evaluate the effects of the implant on the current density distribution in extremely low frequency electric and magnetic fields. The intramedullary nail was chosen because it is one of the longest high conductive implants used in the human body. As such it is expected to alter the electric and magnetic fields significantly. The exposure was a simultaneous combination of inferior to superior electric field and posterior to anterior magnetic field both alternating at 50 Hz with the values corresponding to the ICNIRP reference levels: 5000 V m^?1 for electric field and 100 µT for magnetic flux density. The calculated current density distribution inside the model was compared to the ICNIRP basic restrictions for general public (2 mA m^?2). The results show that the implant significantly increases the current density up to 9.5 mA m^?2 in the region where it is in contact with soft tissue in the model with the implant in comparison to 0.9 mA m^?2 in the model without the implant. As demonstrated the ICNIRP basic restrictions are exceeded in a limited volume of the tissue in spite of the compliance with the ICNIRP reference levels for general public, meaning that the existing safety limits do not necessarily protect implanted persons to the same extent as they protect people without implants. Bioelectromagnetics 30:591–599, 2009. © 2009 Wiley‐Liss, Inc.     

Ex Vivo and In Silico Feasibility Study of Monitoring Electric Field Distribution in Tissue during Electroporation Based Treatments

Magnetic resonance electrical impedance tomography (MREIT) was recently proposed for determining electric field distribution during electroporation in which cell membrane permeability is temporary increased by application of an external high electric field. The method was already successfully applied for reconstruction of electric field distribution in agar phantoms. Before the next step towards in vivo experiments is taken, monitoring of electric field distribution during electroporation of ex vivo tissue ex vivo and feasibility for its use in electroporation based treatments needed to be evaluated. Sequences of high voltage pulses were applied to chicken liver tissue in order to expose it to electric field which was measured by means of MREIT. MREIT was also evaluated for its use in electroporation based treatments by calculating electric field distribution for two regions, the tumor and the tumor-liver region, in a numerical model based on data obtained from clinical study on electrochemotherapy treatment of deep-seated tumors. Electric field distribution inside tissue was successfully measured ex vivo using MREIT and significant changes of tissue electrical conductivity were observed in the region of the highest electric field. A good agreement was obtained between the electric field distribution obtained by MREIT and the actual electric field distribution in evaluated regions of a numerical model, suggesting that implementation of MREIT could thus enable efficient detection of areas with insufficient electric field coverage during electroporation based treatments, thus assuring the effectiveness of the treatment.     

脉冲电磁波对球形大脑作用的理论计算

建立了脑球体模型,赋于脑壳与内部组织不同的电参数,应用时域有限差分法（ＦＤＴＤ）计算了在脉冲电磁波辐射下脑内各点电场的瞬时波形及相应的比吸收率ＳＡＲ。计算结果表明,脉冲电磁波对大脑的瞬态作用时间比脉冲宽度要长,且各点波形不尽相同,但在脑中心有最大的ＳＡＲ,对此讨论了其安全性     

Brain stimulation using electromagnetic sources: theoretical aspects.

We prove that, at the frequencies generally proposed for extracranial stimulation of the brain, it is not possible, using any superposition of external current sources, to produce a three-dimensional local maximum of the electric field strength inside the brain. The maximum always occurs on a boundary where the conductivity jumps in value. Nevertheless, it may be possible to achieve greater two-dimensional focusing and shaping of the electric field than is currently available. Towards this goal we have used the reciprocity theorem to present a uniform treatment of the electric field inside a conducting medium produced by a variety of sources: an external magnetic dipole (current loop), an external electric dipole (linear antenna), and surface and depth electrodes. This formulation makes use of the lead fields from magneto- and electroencephalography. For the special case of a system with spherically symmetric conductivity, we derive a simple analytic formula for the electric field due to an external magnetic dipole. This formula is independent of the conductivity profile and therefore embraces spherical models with any number of shells. This explains the "insensitivity" to the skull's conductivity that has been described in numerical studies. We also present analytic formulas for the electric field due to an electric dipole, and also surface and depth electrodes, for the case of a sphere of constant conductivity.     

Multipactor discharge on a dielectric at different inclination angles of the microwave electric field relative to the dielectric surface

Multipactor discharge on a dielectric is studied numerically and analytically for different inclination angles α of the microwave electric field with respect to the dielectric surface. The power absorbed in the discharge is calculated, and analytic estimates for the average current density of secondary electrons and the average energy of electrons bombarding the dielectric surface are obtained as functions of the angle α and the electron oscillation energy in the microwave field. It is found that the dependence of the absorbed power on the inclination angle of the external microwave field has a minimum at α ～20°–30°.     

Comparative evaluation of hyperthermia heating modalities. I. Numerical analysis of thermal dosimetry bracketing cases

A method for comparing the relative abilities of different hyperthermia heating modalities to properly heat tumors has been developed using solutions of the bio-heat transfer equation. A single measure, the range of absorbed powers that gives acceptable tissue temperature distributions, is used to characterize the ability of a given heating technique to heat a given tumor. An acceptable tissue temperature distribution is one for which (a) the temperatures in the coolest regions of the tumor are above a minimum therapeutic value, (b) the temperatures in the hottest regions of the tumor do not exceed a maximum clinically acceptable value, and (c) the normal tissue temperatures do not exceed maximum clinically acceptable levels. This measure can be interpreted directly in clinical terms as the range of power settings on the power indicator of a heating device for which acceptable tumor heatings will occur. This paper describes the basis of the method and investigates the role of tumor blood perfusion patterns in determining the size of the acceptable power range. Three tumor perfusion patterns are investigated: uniform tumor perfusion, a concentric annulli perfusion model in which the tumor consists of a necrotic core surrounded by two concentric layers of increased perfusion, and a random perfusion distribution model. The results show that, in general, the uniform and annular perfusion models serve as bracketing case patterns. That is, they give acceptable power range values that are upper and lower limits of the acceptable power ranges obtained for the random perfusion patterns. The method is applied to heating patterns that simulate those obtained from a variety of different available heating techniques, and it is found to be valid for all cases studied. The role of normal tissue limiting conditions is also investigated.     

Electrical signals for chondrocytes in cartilage

An important step toward understanding signal transduction mechanisms modulating cellular activities is the accurate predictions of the mechanical and electro-chemical environment of the cells in well-defined experimental configurations. Although electro-kinetic phenomena in cartilage are well known, few studies have focused on the electric field inside the tissue. In this paper, we present some of our recent calculations of the electric field inside a layer of cartilage (with and without cells) in an open circuit one-dimensional (1D) stress relaxation experiment. The electric field inside the tissue derives from the streaming effects (streaming potential) and the diffusion effect (diffusion potential). Our results show that, for realistic cartilage material parameters, due to deformation-induced inhomogeneity of the fixed charge density, the two potentials compete against each other. For softer tissue, the diffusion potential may dominate over the streaming potential and vice versa for stiffer tissue. These results demonstrate that for proper interpretation of the mechano-electrochemical signal transduction mechanisms, one must not ignore the diffusion potential.     

Ecological scaling laws link individual body size variation to population abundance fluctuation

Scaling research has seen remarkable progress in the past several decades. Many scaling relationships were discovered within and across individual and population levels, such as species–abundance relationship, Taylor's law, and density mass allometry. However none of these established patterns incorporate individual variation in the formulation. Individual body size variation is a key evolutionary phenomenon and closely related to ecological diversity and species adaptation. Using a macroecological approach, I test 57 Long‐Term Ecological Research data sets and show that a power‐law and a generalized power‐law function describe well the mean‐variance scaling of individual body mass. This relationship connects Taylor's law and density mass allometry, and leads to a new scaling pattern between the individual body size variation and population abundance fluctuation, which is confirmed using freshwater fish and forest tree data. Underlying mechanisms and implications of the proposed scaling relationships are discussed. This synthesis shows that integration and extension of existing ecological laws can lead to the discovery of new scaling patterns and complete our understanding of the relation between individual trait and population abundance. Synthesis Scaling relationships are useful for community ecology as they reveal ubiquitous patterns across different levels of biological organizations. This work extends and integrates two existing scaling laws: Taylor's law and density‐mass allometry, and derives a new variance allometry between individual body mass and population abundance. The result shows that diverse individual body size is associated with stable population fluctuation, reflecting the effect of individual traits on population characteristics. Confirmed by several empirical data sets, these scaling relationships suggest new ways to study the underlying mechanisms of Taylor's law and have profound implications for fisheries and other applied sciences.     

Evaluation of the impedance technique for cryosurgery in a theoretical model of the head

Bioimpedance is a noninvasive technique that produces information on the electrical characteristics of tissue inside the body from currents injected and electrical potentials measured on the surface of the body. Because freezing causes a large increase in tissue electrical impedance we thought that it may also cause significant changes in the surface electrical potential making the bioimpedance technique suitable for noninvasive monitoring and imaging of cryosurgery. To evaluate the feasibility of the bioimpedance technique in cryosurgery we examined, as a case study, a theoretical model for the electrical potentials during brain cryosurgery. A three-dimensional spherical model was used to calculate the change in the electrical potential distribution in the head as a function of the current source location and the size of the frozen lesion in the brain. The numerical calculations were executed using the finite volume method and the iterative successive over relaxation method. The results demonstrate that, indeed, freezing inside the head produces measurable changes in the electrical potential on the outer surface-the scalp.     

A meshless microscale bone tissue trabecular remodelling analysis considering a new anisotropic bone tissue material law

In this work, a novel anisotropic material law for the mechanical behaviour of the bone tissue is proposed. This new law, based on experimental data, permits to correlate the bone apparent density with the obtained level of stress. Combined with the proposed material law, a biomechanical model for predicting bone density distribution was developed, based on the assumption that the bone structure is a gradually self-optimising anisotropic biological material that maximises its own structural stiffness. The strain and the stress field required in the iterative remodelling process are obtained by means of an accurate meshless method, the Natural Neighbour Radial Point Interpolation Method (NNRPIM). Comparing with other numerical approaches, the inclusion of the NNRPIM presents numerous advantages such as the high accuracy and the smoother stress and strain field distribution. The natural neighbour concept permits to impose organically the nodal connectivity and facilitates the analysis of convex boundaries and extremely irregular meshes. The viability and efficiency of the model were tested on several trabecular benchmark patch examples. The results show that the pattern of the local bone apparent density distribution and the anisotropic bone behaviour predicted by the model for the microscale analysis are in good agreement with the expected structural architecture and bone apparent density distribution.     

Remote sensing as a data source to analyse regional implications of genetically modified plants in agriculture—Oilseed rape (Brassica napus) in Northern Germany

Remote sensing permits the identification of locations and area extent where particular crops are cultivated across larger regions. This requires the availability of crop- and region-specific algorithms. We developed an approach to identify oilseed rape fields in Northern Germany. The remote sensing data sources and main processing steps are described. The derived cultivation density information provides an overview of the fine-scale spatial structure and crop neighbourhood relations in Northern Germany as one of the main oilseed rape cultivation regions in Europe. Geographical Information System (GIS) analyses involving buffer operations allowed to identify those parts of the region, where the highest interaction potential of GM crops and conventional crops would occur if GM varieties were admitted for cultivation. Cultivation density and field sizes in combination were used to indicate the interaction intensity as a marker for observation requirement (environmental monitoring) and for those potential risks that relate to density parameter. Conclusions can be drawn for the feasibility of coexistence measures when neighbouring farmers have to co-operate to keep separation distances between GM crop cultivation and conventional varieties. Together with other data sources, the results of satellite image analysis can be used as input data for up-scaling small-scale model results. Remote sensing data allow to specify, which field density parameter must be chosen to cover the regional variability of cultivation conditions, in particular the regional distribution of field sizes and field density.     

Two concentric protein shell structure with spikes of silkworm Bombyx mori cytoplasmic polyhedrosis virus revealed by small-angle neutron scattering using the contrast variation method

The overall and internal structures of the silkworm Bombyx mori cytoplasmic polyhedrosis virus was investigated by small-angle neutron scattering using the contrast variation method. Data were collected in aqueous buffer solutions containing 0, 50, 75, and 100% D2O in the q range of 0.002 to 0.0774 A-1 at 5 degrees C. The radius of gyration at infinite contrast was estimated to be 336 A. The contrast matching point of the virus was determined to correspond to about 50% D2O level, evidence that the virus is composed of protein and nucleic acid. The virus was basically spherical and had a diameter of about 700 A. The main feature of its structure is the clustering of protein into two concentric shells separated by about 100 A. Most of the RNA moieties are located in the central core and between these two protein shells. However, the distance distribution function P(r) showed a minor distribution beyond a distance of r = 700 A, with a maximum particle distance of the virus of 1350 A. This is indicative of an external structure region with very low scattering density, in addition to the basic spherical structure. This external region is thought to correspond to twelve pyramidal protruding spikes shown by electron microscopic studies.     

Critical polyelectrolyte adsorption under confinement: planar slit, cylindrical pore, and spherical cavity

We explore the properties of adsorption of flexible polyelectrolyte chains in confined spaces between the oppositely charged surfaces in three basic geometries. A method of approximate uniformly valid solutions for the Green function equation for the eigenfunctions of polymer density distributions is developed to rationalize the critical adsorption conditions. The same approach was implemented in our recent study for the "inverse" problem of polyelectrolyte adsorption onto a planar surface, and on the outer surface of rod-like and spherical obstacles. For the three adsorption geometries investigated, the theory yields simple scaling relations for the minimal surface charge density that triggers the chain adsorption, as a function of the Debye screening length and surface curvature. The encapsulation of polyelectrolytes is governed by interplay of the electrostatic attraction energy toward the adsorbing surface and entropic repulsion of the chain squeezed into a thin slit or small cavities. Under the conditions of surface-mediated confinement, substantially larger polymer linear charge densities are required to adsorb a polyelectrolyte inside a charged spherical cavity, relative to a cylindrical pore and to a planar slit (at the same interfacial surface charge density). Possible biological implications are discussed briefly in the end.     

Glow intensity profile in a spherically stratified gas discharge

The glow intensity profile in a spherically stratified gas discharge is measured. It is shown that the boundaries of striations are thin spherical glowing shells, whose thickness is proportional to the striation radius. Based on the analysis of the optical-emission characteristics of spherical striations, the spatial distribution of the electric field in the stratified discharge region is estimated.     

Femoral head apparent density distribution predicted from bone stresses

A new theory relating bone morphology to applied stress is used to predict the apparent density distribution in the femoral head and neck. Cancellous bone is modeled as a self-optimizing material and cortical bone as a saturated (maximum possible bone density) response to stress in the bone tissue. Three different approaches are implemented relating bone apparent density to: (1) the von Mises stress, (2) the strain energy density in the mineralized tissue and (3) a defined closed effective stress (spherical stress). An iterative nonlinear three-dimensional finite element model is used to predict the apparent density distribution in the femoral head and neck for each of the three approaches. It is shown that the von Mises stress (an open effective stress) cannot accurately predict bone apparent density. It is shown that strain energy density and the defined closed effective stress can predict apparent density and that they give predictions consistent with the observed density pattern in the femoral head and neck.     

Similar Spectral Power Densities Within the Schumann Resonance and a Large Population of Quantitative Electroencephalographic Profiles: Supportive Evidence for Koenig and Pobachenko

In 1954 and 1960 Koenig and his colleagues described the remarkable similarities of spectral power density profiles and patterns between the earth-ionosphere resonance and human brain activity which also share magnitudes for both electric field (mV/m) and magnetic field (pT) components. In 2006 Pobachenko and colleagues reported real time coherence between variations in the Schumann and brain activity spectra within the 6–16 Hz band for a small sample. We examined the ratios of the average potential differences (~3 μV) obtained by whole brain quantitative electroencephalography (QEEG) between rostral-caudal and left-right (hemispheric) comparisons of 238 measurements from 184 individuals over a 3.5 year period. Spectral densities for the rostral-caudal axis revealed a powerful peak at 10.25 Hz while the left-right peak was 1.95 Hz with beat-differences of ~7.5 to 8 Hz. When global cerebral measures were employed, the first (7–8 Hz), second (13–14 Hz) and third (19–20 Hz) harmonics of the Schumann resonances were discernable in averaged QEEG profiles in some but not all participants. The intensity of the endogenous Schumann resonance was related to the ‘best-of-fitness’ of the traditional 4-class microstate model. Additional measurements demonstrated real-time coherence for durations approximating microstates in spectral power density variations between Schumann frequencies measured in Sudbury, Canada and Cumiana, Italy with the QEEGs of local subjects. Our results confirm the measurements reported by earlier researchers that demonstrated unexpected similarities in the spectral patterns and strengths of electromagnetic fields generated by the human brain and the earth-ionospheric cavity.